The medicated food is what I recently did for a protozoan that was wiping out my tank, literally. Arrived with new fish, not surprisingly.

I used Metronidazole, which I acquired as a powder under the name Metro+. I mixed this with a quantity of flake food in a zip-lock bag (the oils in the flake will take up the metro) and used it over a period of 14 days. In another bag did the same with some sinking shrimp pellets for the substrate feeders, and this one I made wet in a small jar prior to feeding to get it sinking faster. Dawn had recommended this to me, and it certainly stopped the deaths.

The aquarist is one who must learn the ways of the biologist, the chemist, and the veterinarian.[unknown source]

Something we all need to remember: The fish you've acquired was quite happy not being owned by you, minding its own business. If you’re going to take it under your wing then you’re responsible for it. Every aspect of its life is under your control, from water quality and temperature to swimming space. [Nathan Hill in PFK]

The medicated food is what I recently did for a protozoan that was wiping out my tank, literally. Arrived with new fish, not surprisingly.

I used Metronidazole, which I acquired as a powder under the name Metro+. I mixed this with a quantity of flake food in a zip-lock bag (the oils in the flake will take up the metro) and used it over a period of 14 days. In another bag did the same with some sinking shrimp pellets for the substrate feeders, and this one I made wet in a small jar prior to feeding to get it sinking faster. Dawn had recommended this to me, and it certainly stopped the deaths.

Wow, I am just amazed at the number of protozoan issues that have been popping up lately. That's not a good thing... and makes me wonder what source all of these fish are originating from?

But, with that said, I guess that already is enough info to indicate what I see the problem to be in this situation. The treatment you are in need of is metronidazole laced food. In the case of a tetra I would use a quality tropical flake food such as Tetra.

In the case of the cory catfish I would work with a bottom feeder small pellet and do the same thing... treat the food with metronidazole.

In both cases I would suggest a full 14 day treatment, although I don't know how far gone the tetra is at this point, so I can't make any assurances that the treatment is going to save this fish. A photo of the fish would surely help a lot.

If there are any questions about how to treat the food Byron can help with that as he's just gone through a similar problem and treatment of his own. I would suggest a quarantine tank at this point because I don't know what other fish are all in either of these tanks, so I can't say whether or not this is safe for all of them.

I'm sorry for such a rushed post tonight, as I have been in one other, but I have a very sick macaw that needs attention and don't have much time for anything else at the moment. I will check back in this weekend the first chance I get so I can offer a more detailed post for both cases... so if you wish to list the other fish in each of those tanks I can then let you know if the fish will need to be moved for treatment or not. If there are any questions about the medication to be using and where to order it online please let me know and I can post a link here for you also.

Lastly, I would not be offering these fish medication other than the metronidazole for this problem, so selecting a med that has metronidazole plus other medications in it is not something I suggest. Other medications would only serve to stress the fish by treating for something other than the actual problem and those kinds of medications will not contain enough metronidazole content to do the job that is needed.

Sorry again for my rush, but I need to run for now. I will check in again as soon as I'm able.
Good luck to both of you.

I used Metro+ made by Aquarium Solutions. It happened to be the only product with metronidazole that I could get locally at the time.

Select a prepared dry food that the fish likes to eat (some foods are more "preferred" than others) such as a flake, and place roughly a 2-week ration in a clean zip-lock bag. Add a sprinkling of the metro powder; I didn't measure, just sprinkled some in. Seal the bag and shake it around. Over time, the oils in the flakes will take up the metro. Each day, feed the fish with this food. A period of 14 days.

Corys feed from the bottom, so this gets a bit trickier. If the fish is isolated, you could use the flake and when adding it immediately stir it into the tank so it sinks rapidly. If you use sinking foods like shrimp pellets, do the same process with the bag, but when you feed put a few pellets in a small jar with the Metro and add a tiny bit of water, just enough to get the food wet so it absorbs the water and hopefully some of the metro. I also used Nutrafin sinking tablets which my corys seem to really relish, and being larger they may absorb more Metro when moistened.

If there are other fish in the tank, they can eat this too. The protozoan is contagious, I introduced it with new fish and it killed off quite a few of my older fish rapidly. Feed nothing but medicated foods for the 14 days.

We are fortunate to have a member with Dawn's considerable experience in this area of health. She has saved my fish twice over the past couple of years when nothing else worked. Dawn is going through a rough patch at present as she mentioned, but she is very dedicated to assisting us and I'm sure will be checking back when she can.

The aquarist is one who must learn the ways of the biologist, the chemist, and the veterinarian.[unknown source]

Something we all need to remember: The fish you've acquired was quite happy not being owned by you, minding its own business. If you’re going to take it under your wing then you’re responsible for it. Every aspect of its life is under your control, from water quality and temperature to swimming space. [Nathan Hill in PFK]

Wow, I am just amazed at the number of protozoan issues that have been popping up lately. That's not a good thing... and makes me wonder what source all of these fish are originating from?

But, with that said, I guess that already is enough info to indicate what I see the problem to be in this situation. The treatment you are in need of is metronidazole laced food. In the case of a tetra I would use a quality tropical flake food such as Tetra.

In the case of the cory catfish I would work with a bottom feeder small pellet and do the same thing... treat the food with metronidazole.

In both cases I would suggest a full 14 day treatment, although I don't know how far gone the tetra is at this point, so I can't make any assurances that the treatment is going to save this fish. A photo of the fish would surely help a lot.

If there are any questions about how to treat the food Byron can help with that as he's just gone through a similar problem and treatment of his own. I would suggest a quarantine tank at this point because I don't know what other fish are all in either of these tanks, so I can't say whether or not this is safe for all of them.

I'm sorry for such a rushed post tonight, as I have been in one other, but I have a very sick macaw that needs attention and don't have much time for anything else at the moment. I will check back in this weekend the first chance I get so I can offer a more detailed post for both cases... so if you wish to list the other fish in each of those tanks I can then let you know if the fish will need to be moved for treatment or not. If there are any questions about the medication to be using and where to order it online please let me know and I can post a link here for you also.

Lastly, I would not be offering these fish medication other than the metronidazole for this problem, so selecting a med that has metronidazole plus other medications in it is not something I suggest. Other medications would only serve to stress the fish by treating for something other than the actual problem and those kinds of medications will not contain enough metronidazole content to do the job that is needed.

Sorry again for my rush, but I need to run for now. I will check in again as soon as I'm able.
Good luck to both of you.

At this point there are no other fish in tank, but the Diamonds. I already feed them Tetra flakes. I'm not at home at the moment( summer vacation) soo I can't take a picture.